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"The internal energy of an isolated system is constant (even though that
energy may be transformed from one type to another)." ∆U = q + w Changes in Internal energy
Example: If 1200 joules of heat are added to a
system and the system does 800 joules of work on
the surroundings, what is the :
1. energy change for the system, ∆Esys?
• 2. energy change of the surroundings, ∆Esurr? Change in Internal Energy of
system or ∆U:
∆U > 0 gain of energy
∆U < 0 loss of energy Thermodynamic Terms
Thermodynamic state - set of conditions that specify
all of the properties of the system. Examples The number of moles and identity of each substance.
The physical states of each substance.
The temperature of the system.
The pressure of the system. Isothermal:
Adiabatic: Constant temperature
Zero heat flow (Q = 0) 3 1/7/2014 State functions • State functions - properties of a system that depend only on
the state (Initial and Final states)
– State functions are always written using capital letters. • State functions are independent of pathway.
• An analog to a state function is the energy required to climb a
mountain taking two different paths.
– E1 = energy at the bottom of the mountain
E1 = mgh1
E2 = energy at the top of the mountain
E2 = mgh2
∆E = E2-E1 = mgh2 – mgh1 = mg(∆h) • Some examples of state functions are: – T, P, V, ∆U, ∆H, ∆G, and ∆S
• Examples of non-state functions are:
– n, q, w
In thermodynamics we are often interested in changes in
functions (state functions).
We will define the change of...
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